This invention relates to an apparatus for cutting and stirring curd. Such apparatuses are known from practice and comprise a tank in which a rotatable shaft is situated which carries cutting frames extending radially from the shaft, which cutting frames are mounted on the shaft in staggered relation. The cutting frames each comprise two spaced-apart parallel frame girders, which are mounted by one end on the rotatable shaft and whose other end extends to a point near the wall of the tank. The tank can be arranged horizontally or vertically, the rotatable shaft then being likewise horizontal or vertical.
Arranged between the frame girders is a lattice of longitudinal and transverse knives. The transverse knives extend transversely to the frame girders and are welded to them. The longitudinal knives extend parallel to the frame girders and are mounted on the transverse knives by welding.
Such an apparatus is, for instance, the curd vat marketed by Tetra Pak Tebel under the name of OST4. Such an apparatus is also described, for instance, in U.S. Pat. No. 4,108,058. A variant with two horizontal shafts in a horizontal oval tank is described in U.S. Pat. No. 4,989,504.
All known apparatuses are arranged for stirring and cutting curd which has formed in the tank in that the tank has been filled with milk to which starter and rennet have been added. To that end, the central shaft is driven for rotation, so that the cutting frames move through the curd formed. The cutting frames are usually designed such that the knives and the frame girders form a cutting edge along one edge and are blunt and rounded off along the other edge. Accordingly, rotation of the central shaft(s) in one direction substantially yields a cutting action, while rotation in the other direction substantially yields a stirring action.
A problem presenting itself in the known apparatuses is that they comprise many welds, which must all be polished very well to prevent accumulation of contaminants and bacterial growth. The longitudinal knives can be arranged, for instance, with interspaces of the order of 4 to 5 cm and the transverse knives with interspaces of, for instance, 14.5 to 17.5 cm. A cutting frame can, for instance, have a total width of the order of 50 cm and a length of, for instance, 150 cm. This means that a single cutting frame can comprise, for instance, about 100 rectangular lattice openings, each having four corners where a longitudinal knife or a frame girder is welded to a transverse knife. Each of those welds not only needs to be provided, but also needs to be accurately polished to satisfy the requirements set by government regulations with regard to cleanability. For the welding operation, and in particular also for the polishing operation, however, little space is available within the lattice openings formed by the longitudinal and transverse elements of a cutting frame. As a consequence, the welding work and the polishing work are very time consuming and costly.
In the past, it has been proposed to make the cutting frames of detachable design to obtained a better cleanability. A major drawback of such a solution is that each time a curd vat is to be cleaned, time consuming and cumbersome dismounting activities are necessary.
Accordingly, there is a need for an apparatus of the above-described kind, having a construction such that the necessary welling and polishing work is considerably reduced and simplified, while yet an effective cutting and stirring action and an excellent cleanability remain guaranteed.
According to the invention, to that end, an apparatus for cutting and stirring curd, comprising a curd vat with a shaft drivable for rotation, which shaft carries a number of cutting frames extending radially from the shaft and mounted on the shaft in staggered relation, each cutting frame having frame girders which extend radially from the drivable shaft and between which a lattice work is situated formed from longitudinal knives and transverse knives, the transverse knives being mounted on the frame girders by welding, is characterized in that the transverse knives form openings which are in line, in which the longitudinal knives are received with ample play, and means are provided to substantially prevent displacement of the longitudinal knives in the longitudinal direction.
In the following, the invention will be further described with reference to the accompanying drawings.
FIG. 1 schematically shows in longitudinal cross section an example of a known apparatus for cutting and stirring curd;
FIG. 2 schematically shows the apparatus of FIG. 1 in cross section;
FIG. 3 schematically shows in top plan view an example of a known cutting frame for an apparatus for cutting and stirring curd;
FIG. 4 schematically shows an end view of the cutting frame of FIG. 3;
FIG. 5 schematically shows a section along the line Vxe2x80x94V in FIG. 3;
FIG. 6 schematically shows a top plan view of an example of a cutting frame according to the invention;
FIG. 7 schematically shows a side elevation of the cutting frame of FIG. 6; and
FIG. 8 schematically shows a cross section along the line VIIIxe2x80x94VIII in FIG. 6;
FIG. 9 shows a detail of the cutting frame of FIG. 6;
FIGS. 10 and 11 schematically show examples of the manner in which a transverse knife of a cutting frame according to the invention can receive a longitudinal knife;
FIG. 12 schematically shows a few examples of shapes of a bent longitudinal knife;
FIG. 13 schematically shows an example of a bent transverse knife;
FIGS. 14 and 15 schematically show in side elevation and top plan view an example of a fixing method for a longitudinal knife;
FIGS. 16 and 17 schematically show in top plan view and side elevation an example of an alternative fixing method for a longitudinal knife; and
FIG. 18 schematically shows in top plan view a few examples of shapes of the free end of a longitudinal knife.